A load circuit, which supplies power to a load, such as a lamp or a motor, mounted on a vehicle, includes a battery and an electronic switch (MOSFET, etc.) provided between the battery and the load. The battery, the electronic switch and the load are connected to each other via conductors including electric wires. In the load circuit, a control circuit is provided to turning on and off the electronic switch. The electronic switch is tuned on and off by a drive signal and a stop signal output from the control circuit to switch the load between a drive state and a stop state.
In the load circuit, a fuse is provided to protect the load, the electric wire, the electronic switch, etc. by interrupting the circuit instantaneously when an overcurrent flows through the load. Further, as a current detection circuit having characteristics just equivalent to that of a fuse without using the fuse, a configuration described, for example, in JP-A-2007-19728 (Patent Literature 1) is known.
In a configuration adopted by Patent Literature 1, a current having a magnitude proportional to a current flowing through a power MOSFET used as the electronic switch for driving the load is generated, and the circuit is interrupted when the current exceeds a predetermined threshold current and a voltage produced in an RC circuit formed by a resistor and a capacitor reaches a predetermined threshold voltage.